Attribute history not tracked when using session.merge()

[Sylwester Kardziejonek]

I've noticed that the attribute history of my objects is not tracked. The object comes from session.merge() like it was just freshly retrieved from database.

shipping_id = int(request.matchdict.get('id'))

# Get model from db
db_shipping = db.session.query(m.Shipping).get(shipping_id)

# Create updated instance
updated_shipping = m.Shipping(id=shipping_id, price=999)

# Merge it with session
merged = db.session.merge(updated_shipping)
# I've noticed an actual UPDATE is emitted at this point

# Attributes values are correctly reflected, but the history is all 'unchanged'

# Simply iterates over history of each attribute
changeset(merged)

# History is all 'unchanged'

From the other hand, if I add one line, this works:

shipping_id = int(request.matchdict.get('id'))

# Get model from db
db_shipping = db.session.query(m.Shipping).get(shipping_id)

# When I add this, the history is tracked properly
changeset(db_shipping)

# Create updated instance
updated_shipping = m.Shipping(id=shipping_id, price=999)

# Merge it with session
merged = db.session.merge(updated_shipping)

# Attributes values are correctly reflected, history state is correct

# Simply iterates over history of each attribute
changeset(merged)

def changeset(obj):
    data = {}
    for prop in obj.__mapper__.iterate_properties:
        history = get_history(obj, prop.key)
        if history.has_changes():
            old_value = history.deleted[0] if history.deleted else None
            new_value = history.added[0] if history.added else None
            if new_value:
                data[prop.key] = [new_value, old_value]
    return data

[Mike Bayer]

Hi there -

there's not enough detail to show anything here, no data, no mappings. Here is a demo using your function:

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm.attributes import get_history

Base = declarative_base()


def changeset(obj):
    data = {}
    for prop in obj.__mapper__.iterate_properties:
        history = get_history(obj, prop.key)
        if history.has_changes():
            old_value = history.deleted[0] if history.deleted else None
            new_value = history.added[0] if history.added else None
            if new_value:
                data[prop.key] = [new_value, old_value]
    return data


class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    x = Column('x', Integer)
    y = Column('y', Integer)


e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
s.add(A(x=1, y=2))
s.commit()
s.close()


a1 = s.query(A).first()

# When I add this, the history is tracked properly
# changeset(db_shipping)

# Create updated instance
new_a = A(id=a1.id, x=45, y=4)

# Merge it with session
merged = s.merge(new_a)

# Attributes values are correctly reflected, history state is correct

# Simply iterates over history of each attribute
print(changeset(merged))

output:

#!

{u'y': [4, 2], u'x': [45, 1]}

[Mike Bayer]

please provide a complete example that I can run locally here, see http://sscce.org/ for guidelines, thanks!

[Mike Bayer]

hi there -

I don't doubt that you might be hitting something erroneous but I'd need a complete test script to continue. please reopen if you're able to provide this thanks!

[Sylwester Kardziejonek]

I'm using SqlAlchemy with Pyramid and transaction manager, so maybe there is something about the ecosystem. As soon as I'll get back to this issue I'll try to create better example.